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Old 04-16-2013, 06:47 AM   #1
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Moisture barrier ,insulation questions


Hello everyone, I have three questions , But let me fill you in first on the location of my house and year built . It's located in Northwest Florida Alabama state line built in 1985, brick construction. I purchased the home 8 years ago.


My first question is this , In my vented crawl space they have a vapor barrier on the floor joist for the kitchen area only and on the ground in the kitchen area and on the ground everywhere else , Should the moisture barrier only be on the ground only and about a foot up the wall?


Second question is this, When they installed the insulation 30 years ago ( I'm guessing ) they put a batted R-11 insulation in with the facing towards the ground side ,Shouldn't that be on the floor side being used as a moisture barrier also ?


And finally I noticed some of the insulation is sagging but not falling down is it worth the expense of changing it all out and go with an R-16 or higher?

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Old 04-16-2013, 08:36 AM   #2
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Moisture barrier ,insulation questions


Vapor barrier across the floor should be continuous and sealed to the wall. Whatever height on the wall depends on how buried in the ground that the stem wall is. It should be brought to parallel with the ground level.

As far as the insulation goes, skip the batt insulation and vapor control issues (barrier should be to the warm side, i.e. ground if at all in this case) and go with rigid foam over all the joists.

Seal up the bands, put in unfaced insulation in the joist bays, and cover the whole underside with rigid foam. Best of all of the options (that or spray foaming over the joists).

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Old 04-16-2013, 10:07 AM   #3
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Moisture barrier ,insulation questions


First of all there is no vapor barrier. What you have is a retarder.

Secondly, the vapor retarder goes on the warm side. Insulation is a dynamic system, that absorbs moisture, and gives up moisture, depending on the direction of the vapor drive.

If your cooling period (The number of months you run your AC) is longer than your Heating season, which I suspect is the case where you live, the vapor retarder should be out, not in.

If your heating period is longer, the vapor retarder should be in, not out.
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Old 04-16-2013, 11:24 AM   #4
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Originally Posted by jagans View Post
First of all there is no vapor barrier. What you have is a retarder.

Secondly, the vapor retarder goes on the warm side. Insulation is a dynamic system, that absorbs moisture, and gives up moisture, depending on the direction of the vapor drive.

If your cooling period (The number of months you run your AC) is longer than your Heating season, which I suspect is the case where you live, the vapor retarder should be out, not in.

If your heating period is longer, the vapor retarder should be in, not out.
Vapor Barrier - Vapor Retarder Class I (i.e. poly sheeting) goes on the crawlspace floor and is sealed to the stem walls with foam/sealant.
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Old 04-16-2013, 12:11 PM   #5
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Vapor barrier across the floor should be continuous and sealed to the wall. Whatever height on the wall depends on how buried in the ground that the stem wall is. It should be brought to parallel with the ground level.

As far as the insulation goes, skip the batt insulation and vapor control issues (barrier should be to the warm side, i.e. ground if at all in this case) and go with rigid foam over all the joists.

Seal up the bands, put in unfaced insulation in the joist bays, and cover the whole underside with rigid foam. Best of all of the options (that or spray foaming over the joists).
Thanks for your reply windows. So that I can understand you, the vapor barrier should go continuous on the ground and up the foundation wall/stem wall.to ground level (In what your calling the floor correct ? )

No poly on the floor joist it's self but use foam board on the joist. What would be a good thickness of foam board ? unfaced an R-16 ?
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Old 04-16-2013, 08:08 PM   #6
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Moisture barrier ,insulation questions


1" should be sufficient.
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Old 04-17-2013, 12:27 AM   #7
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Moisture barrier ,insulation questions


Do you have any HVAC/ducting or gas water heater down there? How deep are the floor joists?

Gary
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Old 04-17-2013, 08:29 AM   #8
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Do you have any HVAC/ducting or gas water heater down there? How deep are the floor joists?

Gary

Thank you for the reply WA.I have only one return vent for the A/C ,Also there is a water heater down there.

I also have my well pressure tank down there.

The floor joist are over my head when standing at the low end at the high end when crawling around their about 20" over my head.

No gas at all.
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Old 04-18-2013, 01:11 AM   #9
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Moisture barrier ,insulation questions


If the crawlspace is wet, I usually recommend foamboard on the joists, though it works in warm areas also-fig. 7; BSI-009: New Light In Crawlspaces —

But because of your location, you might think about conditioning it, using 40% less f.b.-#2; http://www.buildingscience.com/docum...ong-from-start

http://www.buildingscience.com/docum...ance-and-codes

Gary

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